1. Field of the Invention
The present invention relates to a gasket used for sealing between confronting surfaces of structural components such as cylinder blocks, cylinder heads and others.
2. Description of the Prior Art
Conventionally, a metal gasket has been widely applied to an automotive engine in sealing, for example, between a cylinder block and a cylinder head, which includes a metal plate having on the surfaces thereof beads or grommets that extend along areas surrounding around cylinder bore holes, the metal plate being enclosed on the surfaces thereof with elastic coating. When squeezing the metal gasket of the conventional structure interposed between the cylinder block and the cylinder head, the metal gasket undergoes more compressive stress at the beads, grommets, folded portions or the like, where the elastic coatings are thus strongly forced against the opposing surfaces. This helps ensure the sealing effect to keep high-temperature combustion gases against the leakage out of the cylinder bore through between the confronting surfaces of the metal gasket and either the cylinder block or cylinder head. The exemplary metal gaskets of the prior art as described just above are disclosed in Japanese Patent Laid-Open Nos. 357371/1992; 89114/1997; and 285086/1996.
Nevertheless, since the metal gasket is usually exposed to the repeated very high-gas pressure impact caused by explosion and combustion inside the cylinder, the cylinder head is displaced with respect to the cylinder block at every high pressure impact whereby the metal gasket is made changed in thickness at the sealing areas around the cylinder bores. That is to say, the prior metal gasket has a disadvantage phenomenon that the beads or corrugations on the metal plate is easily made changed in their height and thus the elastic coatings on the metal plate come in elastic deformation, to thereby let the elastic coating and the beads free of compression.
In accordance with the disadvantage as described just above, it will be said the higher the beads and elastic coatings are in their elasticity, the greater will be the degree of the elastic deformation and, therefore, this causes a major problem of fatigue failure of beads and others. To cope with this problem, conventionally, the metal gaskets have come much more complicated in construction. However, the prior complicated metal gaskets result in lacking in flexibility or adaptability to the diverse designs of the engine.
Moreover, the displacement of the cylinder head in the direction across a clearance between the cylinder head and cylinder block depends on spring constant at the areas of the head-to-block sealing for the cylinder bores. That is to say, greater spring constant, or stiffness, results in less displacement. Thus, the displacement of the cylinder head may be made less when the metal plate is made of material higher in elastic coefficient or formed in the construction more in stiffness, instead of forming the beads or providing the elastic coatings. But if considering the compensation for off-alignment between the confronting surfaces and the uniform squeezing force throughout the confronting surfaces, there has been no metal gasket to seal between the confronting surfaces of the cylinder block and the cylinder head or between the adjoining metal plates in the metal gasket with no provision of elastic members. Today, any elastic member or elastic construction has been thus applied to the metal gaskets.
In technology about the metal gaskets, the restraint of the displacement by making use of the material or construction greater in elastic coefficient is inconsistent with the uniform squeezing force throughout the confronting surfaces of the structural components in favor of the elastic effect. An improved metal gasket does not yet developed, which is inexpensively made of a material or formed with a design, which may resolve both the inconsistent needs described just above.
Alternative to the conventional beads corrugated on the metal plate for the head-to-block sealing, even if any other means is developed, which may undergo plastic deformation along with ensuring the sealing effect, it will be thought that it is possible to make the gasket substantially inelastic or stiff with no reduction of elastic coefficient.
Moreover, if the metal gasket may be free from the complicated construction such as beads corrugated on the metal plates for sealing effect, there causes no problem of fatigue failure that might occur at and nearby beads or corrugations. In addition, no need of plastic-metalworking operation to form the beads on the metal plate results in no need of mould, thus making the metalworking steps simple with less production cost of the metal gasket. Moreover, the improved sealing effect renders the metal plates less in number, thus reducing the production cost of the metal gasket.